Question

如何在swift 3中编写这部分代码？我正在构建一个笔记应用程序，这部分是关于将在tableView单元格中显示的标题

if countElements(item.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceAndNewlineCharacterSet())) > 0


func textViewDidChange(textView: UITextView) {
    //separate the body into multiple sections
    let components = self.txtBody.text.componentsSeparatedByString("\n")
    //reset the title to blank (in case there are no components with valid text)
    self.navigationItem.title = ""
    //loop through each item in the components array (each item is auto-detected as a String)
    for item in components {
        //if the number of letters in the item (AFTER getting rid of extra white space) is greater than 0...
        if countElements(item.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceAndNewlineCharacterSet())) > 0 {
            //then set the title to the item itself, and break out of the for loop
            self.navigationItem.title = item
            break 
          } 
        } 
    }

Answer 1

这应该适合你：

if item.trimmingCharacters(in: .whitespacesAndNewlines).characters.count > 0 {}

Answer 2

这是怎么回事？

extension String {
    func firstNonEmptyLine() -> String? {
        let lines = components(separatedBy: .newlines) 
        return lines.first(where: { 
               !$0.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty })
    }
}

func textViewDidChange(textView: UITextView) {
    self.navigationItem.title = self.txtBody.text.firstNonEmptyLine() ?? "Default title if there's no non-empty line"
}

Answer 3

查询是否存在不属于给定字符集的字符：使用适合该作业的工具

// if the number of letters in the item (AFTER getting 
// rid of extra white space) is greater than 0...

如果您只是想知道String实例item中是否有任何字符<{3}}中的不是（一组unicode标量），没有理由使用trimmingCharacters(in:)方法，而是使用短路方法来查找不在此字符集中的第一个可能的unicode标量

if item.unicodeScalars.contains(where:
    { !CharacterSet.whitespacesAndNewlines.contains($0) }) {
    // ...
}

或者，使用（也是短路）CharacterSet.whitespacesAndNewlines来查找是否可以找到任何属于倒置.whitespaceAndNewlines字符集的字符

if item.rangeOfCharacter(from: CharacterSet.whitespacesAndNewlines.inverted) != nil {
    // ...
}

Swift 3中的countElements

3 个答案: